1. Field of the Invention
The present invention relates to an inspection system for use in the inspection of a plate having a retardation layer and to a method of inspecting such a plate, and particularly to a plate inspection system and a plate inspection method with which irregularities in phase difference caused in a retardation layer can be efficiently detected.
2. Background Art
In recent years, a variety of liquid crystal displays have been brought into practical use. These liquid crystal displays are at a disadvantage in that their viewing angles are narrow as compared with CRT displays. Responsible for this disadvantage is mainly the fact that images displayed on the liquid crystal displays are not seen normally when viewed from oblique directions because of the inversion of contrast that occurs due to leakage of light from those pixels that are supposed to display black. By placing a transparent film that is anisotropic with respect to refractive index (hereinafter referred to as a “retardation film”) on the surface of a liquid crystal cell, there can be obtained a liquid crystal display with a wide viewing angle, which an observer can observe an image displayed on it without suffering leakage of light even from oblique directions (e.g., Patent Document 1).
However, such a retardation film has the problem that since it is bonded to the substrate of a liquid crystal cell with a pressure-sensitive adhesive in the production of a liquid crystal display, the final thickness of the liquid crystal display inevitably gets greater, especially when a laminate of two or more retardation films is used. Another problem with the retardation film is that since it is poor in heat resistance and shrinks with time, it undergoes a change in optical properties.
In view of these disadvantages, it has recently been proposed that a retardation layer formed by three-dimensionally cross-liking a liquid crystalline polymer be placed on a layer contained in a liquid crystal cell (e.g., Patent Document 2). Since such a retardation layer can be laminated directly to the substrate of a liquid crystal cell without using a pressure-sensitive adhesive, it makes possible to produce a thinner liquid crystal display with improved reliability. Especially when such a retardation layer is incorporated into a color filter for use in a liquid crystal color display, it can be subjected to micropatterning. The incorporation of the retardation layer into a color filter is thus particularly useful.
Patent Document 1: Japanese Laid-Open Patent Publication No. 153802/1998
Patent Document 2: Japanese Laid-Open Patent Publication No. 003750/2005